Black Shark

Question
I have a large community tank.  However I am concerned primarily about my black shark (large one at that).  I recently purchased 3 swordtails (about 2 months ago), and about a week or two ago they started "grooming" or picking at the black shark.  Normally the shark would swim away from them, but recently I have found that he is just lying there and waiting for them.  He has (about 3 days ago) developed a white-grey spot on his scales (mid to low abdomen)

Answer
Hi Sarah,
The Black shark might need more hiding places in the form of dark caves. Flowerpots work exceptionally well as hiding places for sharks and other bottom dwelling fish especially.

It is unusual that he is allowing himself to be picked on. Maybe he has nowhere to hide or has given up trying to get away. Maybe he is sick. We can't be for sure. The white-gray spot could be from the swordtails' picking. But it could be fungus growth starting. Just keep a close eye on it and watch for any spreading or "fuzzy" appearance to it. If this happens, isolating him in a treatment tank is best. Jungle Brand's Fungus clear has worked really well for me in the past for fungus treatment.

I would also be sure to to check the water quality just to be sure nothing is wrong. If the tank is recently setup, there can be ammonia or nitrites present which means great problems for the fish. But even established tanks can have water quality issues so the best thing is to test it just as a precaution. Knowing your ammonia, nitrite and nitrate levels are important when your fish don't seem to be acting right.

Best of luck and I hope this helps!
Karen~